Prickle-free blackberry (Rubus subgenus Rubus) canes are strongly preferred by growers due to food and worker safety concerns and damage to fruit from mechanical injury by prickles.

Blackberry is a specialty crop with an increasing share of the fresh berry market.

The growth in demand and rising production costs have resulted in a need for cultivars that are adaptable to many environments and cultural management approaches.

Prickles are a burden in blackberry production systems because they are a food safety concern and can cause mechanical damage to fruit and shorten shelf life.

A common goal of fresh-market blackberry breeding programs is to release cultivars that lack thorns or, more correctly, prickles. Often, these terms are used interchangeably in literature.

Prickles are botanically differentiated from thorns and spines because they are borne of cortical and epidermal cells.

“Blackberry breeders have not had the necessary genetic information to identify why some plants lacked what are technically known as prickles but are commonly called thorns,” said Dr. Margaret Worthington, a researcher at the Arkansas Agricultural Experiment Station.

“All fresh market blackberry varieties are tetraploids, meaning they have four copies of every chromosome as opposed to humans’ two copies.”

“The higher number of copies makes genetic analysis more difficult.”

“No one knew the genetic locus, or the location of a gene on a chromosome, for the prickly trait, making it an obvious target to work on.”

The team’s results reveal the first diagnostic marker for any trait that’s been developed and published in blackberry.

“These are the world’s first publicly available markers developed for fresh-market and processing blackberries,” said Dr. Ellen Thompson, Global Rubus Breeding and Development Director for Hortifrut Genetics.

“Markers save time and money, allowing breeders to make decisions faster — before seedlings are planted in the field.”

The authors used a genome-wide association study to determine the locus responsible for the thornless trait.

They gathered DNA from a total of 374 blackberry varieties, some with the prickly trait and some without.

These DNA samples were then analyzed through genotyping, a highly precise process that involves scanning for and identifying variations in the genetic code that could influence the prickly trait.

If these variations, known as single-nucleotide polymorphisms (SNPs), are significantly associated with the trait, it suggests a gene in that area could be influencing the trait.

These SNPs, also referred to as markers, are what point to the region associated with the trait in question.

“The use of genetic markers is more recently being adopted for blackberries and raspberries, but this type of development is more advanced when it comes to row crops like rice and soybeans,” Dr. Worthington said.

“Genetic markers are used really widely in row crops to select for things like disease resistance, cutting or flowering date, and other traits of interest.”

Another key finding of the study was the lack of genetic variation around chromosome Ra04 leading to a linkage disequilibrium block, or a region where genetic markers are more likely to be inherited together than by happenstance.

For the thornless gene included in this block, this means it is often passed on from parent plant to child plant with many other genes — including undesirable traits like high acidity, lack of cold tolerance and canes that don’t grow upright unless supported.

“In selecting so specifically for thornless plants, these negative traits have been brought in and variation around the locus has been lost,” Dr. Worthington said.

“Conducting crosses with prickly plants could help bring the variation back.”

The team’s paper was published in the journal G3: Genes, Genomes, Genetics.

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Carmen A. Johns et al. Genetic control of prickles in tetraploid blackberry. G3: Genes, Genomes, Genetics, published online March 20, 2025; doi: 10.1093/g3journal/jkaf065